This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A263471 #29 Feb 16 2025 08:33:27
%S A263471 1,9,77,543,3213,16673,86093,503815,3529057,25402097,162303510,
%T A263471 884504882,4156234265,17270407962,65375131342,232901619970,
%U A263471 807191392546,2795912956450,9796747697594,34556445906044,120898966116007,413105921852769,1363586516014222
%N A263471 Total number of positive integers < 10^n with multiplicative digital root value 2.
%C A263471 Partial sums of A263477.
%H A263471 Hiroaki Yamanouchi, <a href="/A263471/b263471.txt">Table of n, a(n) for n = 1..50</a>
%H A263471 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MultiplicativeDigitalRoot.html">Multiplicative Digital Root</a>
%F A263471 A263470(n) + A000027(n) + a(n) + A000217(n) + A263472(n) + A263473(n) + A263474(n) + A000217(n) + A263475(n) + A000292(n) = A002283(n).
%t A263471 Length@ Select[Range[10^# - 1], FixedPoint[Times @@ IntegerDigits@ # &, #] == 2 &] & /@ Range@ 6 (* _Michael De Vlieger_, Oct 19 2015 *)
%o A263471 (PARI) t(k) = {while(k>9, k=prod(i=1, #k=digits(k), k[i])); k}
%o A263471 a(n) = sum(i=1, 10^n - 1, if(t(i) == 2, 1, 0)); \\ _Altug Alkan_, Oct 19 2015
%Y A263471 Cf. A031347, A034049, A051822, A263477.
%K A263471 nonn,base
%O A263471 1,2
%A A263471 _Martin Renner_, Oct 19 2015
%E A263471 a(8) from _Michael De Vlieger_, Oct 19 2015
%E A263471 a(9)-a(23) from _Hiroaki Yamanouchi_, Oct 25 2015